Considerable interest has been shown in the manufacture of emulsions in the increase of sensitivity.
The use of various additives in silver halide photographic emulsions is known as a means of increasing the sensitivity.
Dextran is a typical example of a sugar which increases the sensitivity of a photographic emulsion layer and its use has been disclosed, for example, in U.S. Pat. Nos. 3,063,833 and 3,272,631. However, the following problem arises during development processing when amounts of these materials sufficient for achieving the intended purpose are used.
Specifically, the photographic emulsion layer peels away from the subbing layer, e.g., a layer which is established to ensure adhesion between the photographic emulsion layer and the support, during development processing. The product value of such a photographic material is considerably low.
The method of eliminating such peeling during development processing by simply arranging the proportion of dextran to a binder in the photographic emulsion layer, as disclosed in JP-A-61-69061 is known to be inadequate for maintaining product value (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"). The use of a dextran having a molecular weight of at least 100,000 as suggested in Japanese Patent Application No. 62-313637 is satisfactory as a means of preventing such peeling; however, when the dextran is added, it precipitates out of the coating liquid and the liquid cannot be used for coating over prolonged periods.